Apparatus and method for moving a receive window in a radio access network

ABSTRACT

A method of moving a receiving window in a wireless mobile communication system, wherein the AM RLC of the transmitting side sends information of the last discarded SDU regardless of continuity of the discarded SDUs. The AM RLC of the receiving side checks whether all SDUs from the start point of the receiving window up to the last discarded SDU are successfully received, delivers the SDUs that are successfully received to an upper layer, and discard only those SDUs that are not successfully received.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 12/832,027, filed on Jul.7, 2010, currently pending, which is a continuation of U.S. patentapplication Ser. No. 12/257,793, filed on Oct. 24, 2008, now U.S. Pat.No. 7,826,368, which is a continuation of U.S. patent application Ser.No. 11/771,985, filed on Jun. 29, 2007, now U.S. Pat. No. 7,636,312,which is a continuation of U.S. patent application Ser. No. 10/703,255,filed on Nov. 6, 2003, now U.S. Pat. No. 7,539,197, which pursuant to 35U.S.C. §119(a), claims the benefit of earlier filing date and right ofpriority to Korean Patent Application No. 10-2002-68909, filed on Nov.7, 2002, the contents of which are hereby incorporated by referenceherein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to radio link control (RLC) datatransmission in a UMTS (universal mobile telecommunications system), andmore particularly, to a method for moving a receive window in a radioaccess network.

2. Background of the Related Art

A universal mobile telecommunication system (UMTS) is a third generationmobile communication system that has evolved from a European standardknown as Global System for Mobile communications (GSM) that aims toprovide an improved mobile communication service based upon a GSM corenetwork and wideband code division multiple access (W-CDMA) wirelessconnection technology.

In December 1998, the ETSI of Europe, the ARIB/TTC of Japan, the T1 ofthe United States, and the TTA of Korea formed a Third GenerationPartnership Project (3GPP), which is creating the detailedspecifications of the UMTS technology.

Within the 3GPP, in order to achieve rapid and efficient technicaldevelopment of the UMTS, five technical specification groups (TSG) havebeen created for performing the standardization of the UMTS byconsidering the independent nature of the network elements and theiroperations.

Each TSG develops, approves, and manages the standard specificationwithin a related region. Among these groups, the radio access network(RAN) group (TSG-RAN) develops the standards for the functions,requirements, and interface of the UMTS terrestrial radio access network(UTRAN), which is a new radio access network for supporting W-CDMAaccess technology in the UMTS.

FIG. 1 illustrates a structure of a radio interface protocol between aterminal and the UTRAN according to the 3GPP radio access networkstandards.

Referring to FIG. 1, a radio interface protocol has horizontal layerscomprising a physical layer, a data link layer, and a network layer, andhas vertical planes comprising a user plane for transmitting user dataand a control plane for transmitting control information.

The user plane is a region that handles traffic information of the user,such as voice and Internet protocol (IP) packets, while the controlplane is a region that handles control information for an interface of anetwork, maintenance and management of a call, and the like.

The protocol layers in FIG. 1 can be divided into a first layer (L1), asecond layer (L2), and a third layer (L3) based on the three lowerlayers of an open system interconnection (OSI) standard model. Eachlayer will be described in more detail as follows.

The first layer (L1), namely, the physical layer, provides aninformation transfer service to an upper layer by using various radiotransmission techniques. The physical layer is connected to an upperlayer called a medium access control (MAC) layer, via a transportchannel. The MAC layer and the physical layer send and receive data withone another via the transport channel.

The second layer (L2) includes a MAC layer, a radio link control (RLC)layer, a broadcast/multicast control (BMC) layer, and a packet dataconvergence protocol (PDCP) layer.

The MAC layer provides an allocation service of the MAC parameters forallocation and re-allocation of radio resources. The MAC layer isconnected to an upper layer called the radio link control (RLC) layer,via a logical channel.

Various logical channels are provided according to the kind oftransmitted information. In general, when information of the controlplane is transmitted, a control channel is used. When information of theuser plane is transmitted, a traffic channel is used.

The RLC layer supports reliable data transmissions, and performs asegmentation and concatenation function on a plurality of RLC servicedata units (RLC SDUs) delivered from an upper layer. When the RLC layerreceives the RLC SDUs from the upper layer, the RLC layer adjusts thesize of each RLC SDU in an appropriate manner upon consideringprocessing capacity, and then creates certain data units with headerinformation added thereto. The created data units are called protocoldata units (PDUs), which are then transferred to the MAC layer via alogical channel. The RLC layer includes a RLC buffer for storing the RLCSDUs and/or the RLC PDUs.

The PDCP (Packet Data Convergence Protocol) layer, as a higher layer ofthe RLC layer, allows the data transmitted through a network protocol(such as an IPv4 or IPv6) to be effectively transmitted on a radiointerface with a relatively small bandwidth. To achieve this, the PDCPlayer performs the function of reducing unnecessary control informationused for a wired network, and this type of function is called, headercompression.

A BMC (broadcast/multicast control) layer transmits cell broadcastmessages (hereinafter abbreviated as ‘CB message’) transferred from acore network to terminals through a radio interface. For this, the BMClayer performs the functions of storing, scheduling, and transmittingthe CB messages.

There is a radio resource control (RRC) layer at a lowermost portion ofthe L3 layer. The RRC layer is defined only in the control plane, andhandles the controlling of logical channels, transport channels, andphysical channels with respect to setting, resetting, and releasing ofradio bearers. The radio bearer service refers to a service that thesecond layer (L2) provides for data transmission between the terminaland the UTRAN, and in general, setting the radio bearer refers todefining the protocol layers and the channel characteristics of thechannels required for providing a specific service, as well asrespectively setting substantial parameters and operation methods.

For reference, the PDCP and BMC layers exist in the user plane only,while the MAC and RLC layers can exist in the user plane or the controlplane according to the upper layer connected thereto. Namely, when theRLC layer provides services to the RRC layer, the MAC and RLC layersexist in the control plane. Otherwise, they exist in the user plane.

Moreover, the other the second layers (excluding the MAC layer) have aplurality of entities to guarantee the QoS (quality of service) that isappropriate for each radio bearer (RB). Namely, a multitude of entitiescan exist in one layer, and each entity provides a separate service.

The RLC layer will be explained in more detail as follows. A basicfunction of the RLC layer is to guarantee the QoS of each RB and theircorresponding data transmissions. As the RB service is a service thatthe second layer of the radio protocol provides to higher layers, theentire second layer affects the QoS, and in particular, the RLC layerhas significant influence to the QoS.

The RLC provides an independent RLC entity for each RB in order toguarantee the particular QoS of the RB, and provides three RLC modes,namely, a transparent mode (TM), an unacknowledged mode (UM), and anacknowledged mode (AM) to support various types of QoS. As the three RLCmodes (TM, UM, AM) respectively support different QoS requirements,there are differences in operation and in specific functions.Accordingly, each operational mode of the RLC must be considered in moredetail. The particular RLC for each mode will be referred to as TM RLC,UM RLC, and AM RLC.

In TM, employing a TM RLC, no protocol overhead is added to the RLC SDUthat is transferred from higher layer. As the RLC lets the SDU pass“transparently,” this mode is called transparent mode (TM). Accordingly,the user plane and the control plane perform the following functions. Inthe user plane, because a data processing time at the RLC is short,real-time circuit data transmissions (such as voice and streaming in thecircuit service domain (CS domain)) are handled. In the control plane,because there is no protocol overhead within the RLC, uplinktransmission of RRC messages from an unspecified terminal (UE), anddownlink transmission of RRC messages that are broadcast to allterminals (UE) within a cell are handled.

Meanwhile, unlike the transparent mode, a mode in which protocoloverhead is added at the RLC is called non-transparent mode.Non-transparent mode is divided into unacknowledged mode (UM) that hasno reception acknowledgement for the transferred data, and acknowledgedmode (AM) that has acknowledgement. In UM, employing a UM RLC, a PDUheader including a sequence number (SN) is added to each PDU and thentransferred, in order to allow the receiving side to identify which PDUswere lost during transmission. As such, in UM (employing a UM RLC), theuser plane handles broadcast/multicast data transmissions or real-timepacket data transmissions, such as voice (e.g., VoIP) and streaming inthe packet service domain (PS domain). In the control plane,transmission of those RRC messages that need no acknowledgementresponse, among all RRC messages delivered to a specific terminal orterminal group within a cell region, is handled.

As in UM, in AM (employing an AM RLC) a PDU header including SN is addedto construct a PDU. However, unlike the UM, in AM, a receiving sideprovides reception acknowledgement of the PDU sent from a transmittingside. In AM, the receiving side provides acknowledgement in order torequest re-transmission of any PDUs that have not been properlyreceived. This function of re-transmission is the most distinguishingcharacteristic in AM RLC. Thus, the object of AM RLC is to guaranteeerror-free data transfers through re-transmissions. To achieve thisobject in AM (employing an AM RLC), transmission of non-real-time packetdata such as TCP/IP in the PS domain is handled by the user plane, andtransmission of RRC messages that absolutely need acknowledgement, amongall the RRC messages transmitted to a specific terminal, is handled bythe control plane.

Considering the direction of data communication, TM RLC and UM RLC areused in uni-directional communication, while AM RLC is used inbi-directional communication because of the necessary feedback(acknowledgement) from a receiving side. Bi-directional communication ismainly used in point-to-point communication, whereby AM RLC usesdedicated logical channels only. Regarding the structural differences,in AM RLC, a single RLC entity performs both transmission and reception,whereas in TM RLC and UM RLC, a RLC entity exists at the transmissionside and a RLC entity exists at the reception side.

The AM RLC requires a more complicated structure and data-processingtechniques due to the re-transmission function. In AM RLC, are-transmission buffer is required in addition to a transmission bufferto manage re-transmission. The AM RLC performs various functions, suchas using a “transmitting/receiving window” for flow control, performing“Polling” in which the transmitting side requests status informationfrom a peer RLC entity at the receiving side, providing a “statusreport” in which the receiving side reports its buffer status to a peerRLC entity at the transmitting side, creating a “status PDU” forcarrying status information, performing “Piggyback” in which a statusPDU is inserted into a data PDU to increase data transmissionefficiency, and the like. Moreover, the AM RLC needs various protocolparameters, state variables, and a timer to support its variousfunctions.

One of the main functions of a RLC is the SDU discard function, wherebycertain RLC SDUs (such as “old” SDUs), among the SDUs stored at thetransmitting side RLC entity, are discarded to prevent overloading ofthe RLC buffer. The SDU discard function plays a significant role inguaranteeing the QoS of a RB service provided by the RLC. Typically, thetransmitting side discards certain SDUs by using scheme employing atimer or a scheme employing a limited number of re-transmissions.

The timer scheme is used in all three kinds of RLC modes (TM, UM, andAM). A transmitting side RLC entity operates a timer (e.g., a discardtime) for measuring the time (duration) that each RLC SDU remains at theRLC layer, each RLC SDU being received from an upper layer. If aparticular SDU fails to be properly transmitted upon expiration of timeperiod set by the timer, that SDU is discarded and all SDUs between thebeginning of a transmitting window and the corresponding SDU arediscarded as well.

The limited number of re-transmissions scheme is used in AM RLC only. Ifthe transmission and re-transmission of a particular RLC PDU continue tobe unsuccessful and the maximum (limit) number of re-transmissions isreached, a transmitting side RLC entity discards any SDU that includesat least a portion of the corresponding RLC PDU. This operation isdescribed in more detail below.

The RLC SDU transferred down to the AM RLC layer at the transmittingside is converted into a RLC PDU to be stored in a buffer. At this time,a counter (e.g., VT (DAT)) for counting the number of transmissions foreach RLC PDUs begins its count operation. The VT (DAT) is incremented by‘1’ each time the RLC PDU (that the VT (DAT) is responsible for) istransmitted. If the transmission of a particular RLC PDU continues to beunsuccessful, and the VT (DAT) reaches the maximum (limit) number ofretransmissions (MaxDAT), the AM RLC discards all SDUs included in atleast a portion of the corresponding PDU, as well as all SDUs between abeginning of a transmitting window and the corresponding SDU.

In case the transmitting side AM RLC discards at least one RLC SDU, sucha discard is notified to the receiving side AM RLC so that the receivingwindow of the receiving side is moved. The receiving window can be movedbecause the receiving side no longer needs to stand by and wait for theSDU that has now been discarded and thus would not be transmitted. Here,this type of operation can be referred to as a ‘Move Receiving Window(MRW)’ function.

The transmitting side sends an MRW message to the receiving side formoving the receiving window. Here, the MRW command does not specify thelocation to which the receiving window should actually move to, but onlyprovides information that a particular SDU has been discarded at thetransmitting side. Upon receiving the MRW message, the receiving sideappropriately moves the receiving window based on the information of thediscarded SDU.

A procedure of moving a receiving window is called a MRW procedure. TheMRW procedure includes the steps of transmitting a MRW command from thetransmitting side, moving the receiving window by the receiving side andtransmitting receiving window move information to the transmitting side,and moving the transmitting window at the transmitting side. Theoperation of each of these steps is explained in detail as follows. Forbetter understanding, the explanation begins with the step performed bythe transmitting side of receiving an SDU from a higher layer.

Construction of PDU from SDU

Once the SDUs are delivered from a higher layer, the transmitting sideAM RLC performs segmentation and concatenation on the SDUs (which may beof different sizes) to construct an AM data (AMD) PDU having apredetermined size. The AMD PDU includes a header added to a payload.The payload consists of a portion of an SDU or at least one or moreSDUs. The header consists of a sequence number (SN) of the PDU and alength indicator (LI) indicating the location of a boundary of the SDUif such boundary exists.

FIG. 2 shows an example of how PDUs are constructed from SDUs.

Referring to FIG. 2, it is assumed that the 1^(st) to 32^(nd) SDUscarried on the 1^(st) to 20^(th) PDUs have already been successfullytransmitted. When subsequent SDUs are delivered down to the AM RLC, theAM RLC performs segmentation or concatenation on the SDUs (that may beof different sizes) to construct AMD PDUs of a predetermined size. InFIG. 2, only the 33^(rd) to 39^(th) SDUs are shown. However, it can beunderstood that additional SDUs may continue to be delivered and thatthe AM RLC continues to construct additional PDUs for the descendingSDUs. Furthermore, the AM RLC attaches the SN of the PDU to the AMD PDUheader. If a boundary of the SDU exists within a constructed PDU, anindicator LI indicating the location of the boundary is also added tothe AMD PDU header.

FIG. 3 is an exemplary diagram of showing the processing of the 21^(st)to 23^(rd) AMD PDUs among the constructed AMD PDUs in FIG. 2.

Referring to FIGS. 2 and 3, it can be understood that the 21^(st) PDUconsists of a portion of the 33^(rd) SDU (SDU 33), whereby no boundaryof the 33^(rd) SDU (SDU 33) exists within the 21^(st) PDU. Hence, the21^(st) PDU simply consists of an SN (in the header) and a portion ofSDU 33. Next, the 22^(nd) PDU consists of an end portion of SDU 33, theentirety of SDU 34, and a beginning portion of SDU 35, whereby two SDUboundaries exist within the 22^(nd) PDU. Thus, two LI fields (LI 33 andLI 34) indicating the respective SDU boundaries are added to the header.For the 23^(rd) PDU, since one boundary between SDU 35 and SDU 36 existswithin the 23^(rd) PDU, a corresponding LI field is added to the header.

PDU Storage

Each constructed AMD PDU is stored in a transmission buffer of the AMRLC, and simultaneously stored in a re-transmission buffer for possiblere-transmission that may take place at a later time. The differencebetween the transmission and re-transmission buffers lies in that thePDU having been transmitted once is removed from the transmissionbuffer, but is stored in the re-transmission buffer until that PDU issuccessfully transmitted. FIG. 4 shows an example of how the AM RLCconstructs and stores the AMD PDU in the transmission andre-transmission buffers.

PDU Transmission

The transmitting side AM RLC transmits the constructed PDUs to thereceiving side AM RLC of the peer AM RLC entity. When the transmittingside AM RLC transmits AMD PDUs, all PDUs are not transmitted at once, asonly those PDUs within a transmitting window can be transmitted. Thereason that the AM RLC employs a transmitting window and a receivingwindow to transmit and receive PDUs is to manage those PDUs that need tobe re-transmitted. For this, the transmitting side only transmits thosePDUs in the transmitting window, and the receiving side only receivesthose PDUs in the receiving window. Here, a “window” represents a rangeof PDU SN values, whereby the PDUs in the receiving window refer tothose PDUs having SN values within the range of PDU SN valuescorresponding to the receiving window.

The size of the transmitting/receiving window is set when the RLC entityis created, and its range (SN value range) varies while PDUs aretransmitted and received. The start point and end point (i.e.,boundaries) of the transmitting window and receiving window are definedas follows:

-   -   Transmitting Window        -   Start point: the SN of the first PDU of which an ACK should            be received next in-sequence from the receiving side.        -   End point: the SN of the first PDU among the PDUs that            cannot be transmitted.    -   Receiving Window        -   Start point: the SN of the first PDU that must be received            next in-sequence.        -   End point: the SN of first PDU among the PDUs that cannot be            received.

As can be seen from the above definitions, the transmitting side enablesthe transmission of only those PDUs having SNs within a range from thestart point to the next-to-last end point (“endpoint—1”). The PDUshaving SNs at and after the end point can be transmitted only after thetransmitting window is updated. Updating of the transmitting windowtakes place when the ACK for the first in-sequence PDU is received fromthe receiving side.

In a similar manner, the receiving side enables the reception of onlythose PDUs having SNs within a range from the start point to thenext-to-last end point (“endpoint—1”). If a PDU having an SN that isoutside of such a range is received, the receiving side immediatelydiscards such PDU. Updating of the receiving window takes place when thefirst in-sequence PDU is successfully received.

It should be noted that the size of the transmitting window and thereceiving window is defined as the interval (size) between the startpoint and the end point. For example, assuming that the size of thetransmitting/receiving window is 10 and the 1^(st) to 20^(th) PDUs havebeen successfully transmitted, the range of the transmitting window is21˜31, and also, the range of the receiving window is 21˜31.

At the transmitting side, because the 21^(st) PDU is the first PDU ofwhich an ACK should be received in-sequence, the transmitting window canbe updated only if the successful transmission of the 21^(st) PDU isconfirmed. Likewise, at the receiving side, because the 21^(st) PDU isthe first PDU to be received in-sequence, the receiving window can beupdated only if the successfully receiving of the 21^(st) PDU isconfirmed.

If an endpoint of the transmitting/receiving window is 31, thetransmitting side can only transmit the 21^(st) to 30^(th) PDUs.Accordingly, the receiving side can only receive the 21^(st) to 30^(th)PDUs as well. The receiving side immediately discards any PDU having anSN that is out of range, as soon as such PDU is received. Updating ofthe transmitting window and the receiving window is continuouslyperformed while the AMD PDUs are transmitted/received, as is shown inFIG. 5.

FIG. 5 shows an example for transmitting/receiving AMD PDUs and updatingthe transmitting window and the receiving window, in which all PDUs, upto the 20^(th) PDU, are assumed to be successfully transmitted and boththe transmitting window and the receiving window having a range of21˜31.

Referring to FIG. 5, a transmitting side constructs PDUs using the SDUsdelivered from a higher layer and transmits the constructed PDUs to thereceiving side. Here, the range of a transmitting window is 21˜31,whereby only those PDUs within such a range are transmitted. Theconstructed PDUs are sequentially transmitted according to their SNs,and one or more PDUs can be transmitted within one transmission timeinterval (TTI). Although only the 21^(st) to 28^(th) PDUs are shown inFIG. 5, PDU transmission continues to take place, whereby additionalPDUs can be further transmitted if they have SNs that fall within therange.

The receiving side waits for PDU reception with a receiving windowhaving a range between 21˜31. For those PDUs within the range, properreception is possible. However, if a PDU that is outside the range isreceived, the receiving side regards such PDU as erroneous and thusimmediately discards such PDU. Since the transmitting side sequentiallytransmits PDUs, the receiving side sequentially receives these PDUs aswell. The receiving side updates the receiving window to a range of22˜32 once the 21^(st) PDU is properly received. Thereafter, uponproperly receiving the 22^(nd) PDU, the receiving side updates thereceiving window to 23˜33. Namely, updating of the receiving windowtakes place only if a PDU that is supposed to be received in-sequence isproperly received.

However, if the 24^(th) PDU is received when the receiving window hasbeen updated to 23˜33, the receiving window will not be updated anyfurther. Hence, the receiving side receives subsequent PDUs while thereceiving window is fixed at a range of 23˜33. FIG. 5 shows an examplewhere the 23^(rd), 26^(th), and 27^(th) PDUs are lost duringtransmission. The receiving side sends a status report regarding thereceived PDUs to the transmitting side. Here, it is assumed that thestatus report is sent at the time when the 28^(th) PDU is received. Thereported status information provides that among the 21^(st) to 28^(th)PDUs, the 23^(rd), 26^(th), and 27^(th) PDUs have not been properlyreceived, and other PDUs have been properly received.

Upon receiving the status report from the receiving side, thetransmitting side deletes the successfully transmitted PDUs from there-transmission buffer, then updates the transmitting window, andprepares re-transmission of the transmission-failed PDUs. Namely, afterdeleting the 21^(st), 22^(nd), 24^(th), 25^(th) and 28^(th) PDUs (i.e.,the properly transmitted PDUs) from the re-transmission buffer, thetransmitting side maintains the 23^(rd), 26^(th), and 27^(th) PDUs inthe re-transmission buffer and prepares for re-transmission. In FIG. 5,it is assumed that PDUs are additionally constructed (up to the 34^(th)PDU) after the PDUs (up to the 28^(th) PDU) have been properlytransmitted. As PDU transmission occurs sequentially, the 23^(rd),26^(th), and 27^(th) PDUs are re-transmitted and then the 29^(th) to32^(nd) PDUs are transmitted for the first time. Here, because the33^(rd) and 34^(th) PDUs are outside the range of the transmittingwindow, they are stored in the transmission buffer and await subsequenttransmission.

Following the above-explained procedure, the receiving side sequentiallyreceives PDUs. If the 23^(rd) PDU is received (as a result ofre-transmission from the transmitting side), the start point of thereceiving window is moved to the SN (i.e., SN=26) of the PDU to bereceived first in-sequence, because the 24^(th) and 25^(th) PDUs werealready properly received. Namely, at the time of receiving 23^(rd) PDU,the receiving window is updated to 26˜36. Once 26^(th) PDU is received,the receiving window is again updated to 27˜37.

However, if the 27^(th) PDU is not received thereafter, but the 29^(th)PDU is received instead, the receiving window maintains its range as27˜37 and is not 30^(th), updated. FIG. 5 shows that the 27^(th), and31^(st) PDUs are not received among the PDUs up to the 32^(nd) PDU.Specifically, the 27^(th) PDU failed to be transmitted twice (that is,one re-transmission failed). When receiving the 32^(nd) PDU, assumingthat the receiving side sends a status report, the receiving side havingreceived the PDUs up to the 32^(nd) PDU will send a status reportindicating the failure to receive the 27^(th), 30^(th), and 31^(st)PDUs.

Discard of SDU

Assuming that transmission of the 23^(rd) PDU continues to fail, if thePDUs as shown in FIG. 5 are constructed with the SDUs in FIG. 2, thetransmission failure of the 23^(rd) PDU means that the 35^(th) and36^(th) SDUs will also have transmission failures. The discarding ofSDUs differs for the timer scheme and for the limited number ofre-transmissions scheme, thus these will be explained in more detail asfollows.

Upon receiving an SDU from a higher layer, the AM RLC immediatelyoperates a discard timer for the SDU. Here, the discard timer operatesfor each SDU. The discard timer stops operating the moment the SDU issuccessfully transmitted and the discard timer assigned to that SDU isremoved (expires). Here, ‘successfully transmitted’ means that an ACKsignal (informing that all PDUs having at least a portion of an SDU havebeen successfully received) is received from the receiving side. As theSDUs are sequentially delivered to the RLC, the discard timersequentially expires as well. In FIG. 2, if the 23^(rd) PDU is notsuccessfully transmitted by the time the discard timer of the 35^(th)SDU expires, the 35^(th) SDU is discarded at the moment when the discardtimer expires.

Here, it is important to note that the SDU is discarded, and not thePDU. Since a PDU is constructed with segmented and/or concatenated SDUs,one SDU may be entirely within one PDU or one SDU may span acrossseveral PDUs. In any case, the discard of the SDU means that allcorresponding portions of the SDU are discarded from all PDUs thatcontain any portion of that SDU.

For example, referring back to FIG. 2, even if the 22^(nd) PDU succeedsin transmission, a transmission failure of the 23^(rd) PDU results inthe discarding of the 35^(th) SDU. Hence, a portion of the 35^(th) SDUin the 22^(nd) PDU is discarded as well. Moreover, it is also importantto note that the 23^(rd) PDU is not discarded even if the 35^(th) SDU isdiscarded. Having a portion of the 36^(th) SDU as well as a portion ofthe 35^(th) SDU, the 23^(rd) PDU continues to be re-transmitted untilthe discard timer of the 36^(th) SDU expires. Even if the 23^(rd) PDU isre-transmitted while the 35^(th) SDU has been discarded, there-transmission does not exclude the portion of the 35^(th) SDU. Theconstruction of the re-transmitted PDU should be equal to that of theoriginally transmitted PDU.

When SDUs are delivered down from a higher layer, they may descendsimultaneously despite sequential delivery. If the 35^(th) and 36^(th)SDUs are delivered almost simultaneously, the discard timers of the35^(th) and 36^(th) SDUs may expire almost at the same time. In such acase, the 35^(th) and 36^(th) SDUs are discarded almost at the sametime, and re-transmission of the 23^(rd) PDU is interrupted as well asthat of the 24^(th) PDU that includes the 36^(th) SDU. As the 25^(th)PDU includes a portion of the 37^(th) SDU of which the discard timer hasyet to expire, the 25^(th) PDU continues to be re-transmitted until thediscard timer of the 37^(th) SDU expires. As mentioned in the foregoingexplanation, a construction of the re-transmitted 25^(th) PDU is thesame as that of the originally transmitted PDU.

The discard method using the timer scheme performs the discard of SDUsusing the expiration of the discard timer, by which the discard of SDUsoccur sequentially. However, in the limited number of re-transmissionsscheme, an SDU is discarded if the PDU that has been re-transmitted (asmany times as the maximum (limit) number of re-transmission schemeallows) is not successfully transmitted. Hence, unlike in the timerscheme, all SDUs including at least a portion of the corresponding PDUare simultaneously discarded according to the limited number ofre-transmissions scheme.

For example, as shown in FIG. 2, if the 23^(rd) PDU fails to be properlytransmitted even when the maximum (limit) number of re-transmissions isreached, the 35^(th) and 36^(th) SDUs are simultaneously discarded.However, because this scheme is also for discarding SDUs, the proceduresthereafter are the same of those of the timer scheme in that two SDUsare discarded at almost the same time. Namely, a corresponding portionof the 22^(nd) PDU is discarded due to the discarding of the 36^(th)SDU, while the 24^(th) PDU is discarded due to the discarding of the36^(th) SDU, despite the fact that the re-transmissions of the 24^(th)PDU has yet to be completed because the maximum (limit) number ofre-transmissions has not yet been reached. However, the 25^(th) PDUincluding the 37^(th) SDU therein continues to be re-transmitted untilthe maximum (limit) number of re-transmissions is reached.

Transmission of SDU Discard Information

A MRW procedure that is directly related to the present invention isexplained as follows. After discarding an SDU, the transmitting side AMRLC informs the receiving side of the discarded SDU through a MRWcommand for moving the receiving window. In this case, the MRW commanddoes not directly indicate the position to which the receiving windowshould move, but only informs the SDU discard information, whereby thereceiving side moves the receiving window to an appropriate positionbased on the discard information.

Information that indicates an end portion of the SDU discarded by thetransmitting side is included in the MRW command that is transmitted bythe transmitting side. In order to indicate the end portion of the SDU,the MRW command should include information related ‘to which PDU the endportion of the SDU belongs’ and ‘to which portion in the PDU the endportion of the SDU belongs’. Hence, the MRW command consists of a SN ofPDU to which the end portion of the discarded SDU belongs, and anindicator indicating an end of the discarded SDU in the PDU.

When at least two SDUs are discarded, the MRW command carriesinformation about the last discarded SDU. This is because the positionto which the receiving window has to move is located after the end ofthe last discarded SDU. Moreover, as explained in the foregoingdescription, when a certain SDU is discarded, all SDUs between the startpoint of the transmitting window and the corresponding SDU are discardedas well. Hence, the receiving side only receives the information of thelast discarded SDU so as to know what SDUs have been discarded at thetransmitting side.

When a higher layer requests information about other discarded SDUs, aswell as the information of the last discarded SDU, the MRW command canoptionally inform such information. However, for the other SDUs, insteadof the last SDU, the SN of the PDU (where the end portion of thediscarded SDU exists) is informed, but an indicator indicating an end ofthe corresponding SDU in the PDU is not informed. This is because theinformation about the other discarded SDUs does not affect the receivingwindow movement, and because these other SDUs are consecutivelydiscarded.

FIG. 6 is a conceptual diagram of the structure of a MRW command, inwhich ‘N’ is the number of discarded SDU information that is carried byMRW command, and the current UMTS standard set this number to be amaximum of 15.

Referring to FIG. 6, a basic MRW command contains information about anend portion of the N^(th) discarded SDU. Additionally, another discardinformation about the SDUs between 1 to N−1 (i.e., SDU 1 to SDU (N−1))can be optionally added.

In FIG. 6, the uppermost field is the number of the PDU SNs included inthe MRW command and is equal to ‘N’. It is important to note that N isnot the number of SDUs substantially discarded in the transmitting side,but the number of SDU discard information carried in the correspondingMRW command.

Namely, if the MRW command includes the SN of PDU where an end portionof the N^(th) SDU exists, the MRW command includes one SDU discardinformation, such that the count is 1. When including all discardinformation of 1^(st) to N^(th) SDUs, the MRW command includes N SDUdiscard information so that the number is N. The reason why a value of Nis notified is that the receiving side is informed whether optional SDUdiscard information of 1˜(N−1) exists or not when receiving the MRWcommand. Also, indicator information that indicates where the endportion of the N^(th) SDU is located within the PDU, is always includedat the end of the MRW command.

Referring to FIGS. 2 and 5, an example of how a MRW command may beactually structured is explained as follows. First, it is assumed thatthe 23^(rd) PDU is not successfully transmitted continuously or for anextended period of time, such that the 35^(th) and 36^(th) SDUs aresimultaneously discarded. In this case, a start point of thetransmitting window is at the 23^(rd) PDU as explained in the foregoingdescription. In such a case, the MRW command is configured as shown inFIG. 7.

Namely, if the 35^(th) and 36^(th) SDUs are discarded due to thetransmission failure of the 23^(rd) PDU, the MRW command for thissituation consists of PDU SN=23 of discard information of the 35^(th)SDU, PDU SN=25 of discard information of the 36^(th) SDU, and anindicator indicating an end of the 36^(th) SDU. Here, as explained inthe foregoing description, the discard information of the 35^(th) SDUcan be optionally inserted by a request of the higher layer and a count(number) field value of the uppermost PDU SN is correspondinglyadjusted.

Moving the Receiving Window and Transmitting Move Information

Upon receiving a MRW command, the receiving side discards all SDUs froman SDU existing at a start point of a receiving window to a last SDUinformed by the MRW command, and correspondingly moves the receivingwindow. The moved position of the receiving window varies according towhether the PDUs (that include the SDUs after the discarded SDU) arereceived or not.

In any case, the basic principle is that the start point of thereceiving window is moved to the SN of the PDU that is first receivedin-sequence after excluding the discarded SDUs. Hence, the movedposition of the receiving window may be the PDU that includes an endportion of the last discarded SDU informed by the MRW command or the PDUthat follows after subsequent PDUs have been successfully received. Thereceiving side consecutively discards the SDUs from the start point ofthe receiving window to correspond to the MRW command, moves thereceiving window, and then informs the transmitting side of the movedposition of the receiving window. In this case, the start point of thereceiving window is the SN of the PDU to be first received in-sequence.

The moved position of the receiving window is explained by reference tothe MRW command in FIG. 7 as an example. Referring back to FIG. 5, thereceiving side successfully receives all PDUs up to the 22^(nd) PDU, butfails to receive the 23^(rd) PDU, whereby the start point of thereceiving window is the 23^(rd) PDU. Assuming that the 24^(th) to28^(th) PDUs are successfully received, if the MRW command shown in FIG.7 is received, the receiving side discards all the SDUs from the startpoint of the receiving window up to the last discarded SDU. Namely, allSDUs from the 35^(th) SDU corresponding to the start point of thereceiving window up to the 36^(th) SDU (which is the last PDU informedby the MRW command) are discarded. Specifically, in FIG. 2, an endportion of the 22^(nd) PDU (that includes the 35^(th) SDU) is discarded,the 23^(rd) PDU fails to be received, the 24^(th) PDU is entirelydiscarded, and a beginning portion of the 25^(th) PDU (that includes36^(th) SDU) is discarded.

Thereafter, the PDUs up to the 28^(th) are successfully received,whereby the start point of the receiving window moves to the 29^(th) PDUto be first received in-sequence. The receiving side then notifies thetransmitting side that the receiving window has moved to the 29^(th)PDU.

In particular situations, the position of the receiving window mayalready proceed further than the PDU specified by the MRW command. Sucha situation occurs when the ACK information is lost during transmission,even if the receiving side having properly received the PDU sends theACK information to the transmitting side. In this case, the receivingside successfully received the PDU and correspondingly updated thereceiving window. Yet, the transmitting side fails to receive ACKinformation for the transmitted PDU, thereby failing to update itsreceiving window. Hence, the start point of the receiving window isbehind the start point of the transmitting window.

For example, referring to FIG. 7, the receiving side successfullyreceived all the PDUs up to the 28^(th) PDU and updated the start pointof the receiving window to the 29^(th) PDU. However, the ACK informationfor the 23^(rd) PDU is consecutively lost during transmission, wherebythe start point of the transmitting window may be held at the 23^(rd)PDU. In this case, if the transmitting side discards the 35^(th) and36^(th) SDUs, and transmits the SDU discard information to the receivingside, the SDU discard information is of no use, because the receivingwindow of the receiving side has already been moved to the 29^(th) PDU.

Hence, when the receiving window has already moved, i.e., when thediscard information of the corresponding SDU is received after thesuccessfully received SDU is delivered to the higher layer, thereceiving side ignores this information and informs the transmittingside of a current position of the receiving window. Yet, the receivingside may not discard the SDU that was discarded by the transmittingside. Namely, if the discard information for the SDU that wassuccessfully received and delivered to the higher layer is received, thecorresponding SDU cannot be discarded because the corresponding SDU wasalready delivered to the higher layer. The receiving side may onlyinform the higher layer of the information that the corresponding SDUwas discarded in the transmitting side.

Transmitting Window Move

Upon receiving the window move information from the receiving side, thetransmitting side moves the start point of the transmitting window tothe same position as the start point of the receiving window. The PDUcorresponding to the start point of the transmitting window may bealready transmitted before the receiving window move information. Insuch case, the transmitting side does not transmit the corresponding PDUand awaits the ACK/NACK status report from the receiving side. If thePDU corresponding to the start point of the transmitting window is nottransmitted beforehand, the transmitting side starts to transmit fromthe corresponding PDU.

In the related art method, after receiving the MRW command, thereceiving side discards all SDUs from the start point of the receivingwindow up to the last discarded SDU informed by the MRW command, wherebyvarious problems are created if the SDUs are discontinuously discardedin the transmitting side.

FIG. 8A is a diagram of explaining how a discontinuous SDU discard takesplace in normal data transmitting and receiving.

First, assuming that the PDUs up to the 20^(th) PDU are successfullytransmitted, the start points of transmitting and receiving windows maybe located at the 21^(st) PDU. If the SDUs are delivered to thetransmitting side RLC while such a status is maintained, the RLCsegments and/or concatenates the SDUs to construct PDUs and thentransmits the constructed PDUs to the receiving side.

FIG. 8A is a diagram of transmitting the 21^(st) to 28^(th) PDUs fromthe transmitting side. In this case, the PDUs up to the 30^(th) PDU canbe substantially transmitted. Yet, the SDUs are sequentially delivereddown to RLC. Hence, it is assumed that the PDUs from the 29^(th) PDU arenot constructed yet at the moment of transmission from the transmittingside.

In FIG. 8A, the receiving side fails to receive the 23^(rd), 26^(th),and 27^(th) PDUs among the 21^(st) to 28^(th) PDUs transmitted throughthe above-described process, because of losses during transmission andsucceeds in receiving the rest of the PDUs. After successfully receivingthe 21^(st) and 22^(nd) PDUs, the receiving side updates the start pointof the receiving window to the 23^(rd) PDU. Yet, no additional receivingwindow updating takes place since the 23^(rd) PDU has not been received.Once the receiving side transmits status information for the 21^(st) to28^(th) PDUs to the transmitting side, the transmitting side deletes the21^(st), 22^(nd), 24^(th), 25^(th) and 28^(th) PDUs from a buffer,updates the start point of the transmitting window to the 23^(rd) PDU,and then awaits subsequent transmission.

FIG. 8B is a diagram explaining a procedure of the transmitting side forupdating the transmitting window to 23˜33, and then performs subsequenttransmission. Here, the PDUs are transmitted in order of the 23^(rd),26^(th), 27^(th), 29^(th), 30^(th), 31^(st), and 32^(nd) PDUs, whereinthe 23^(rd), 26^(th), and 27^(th) PDUs require re-transmission. Itshould be noted that even though the PDUs from the 33^(rd) PDU areconstructed, they cannot be transmitted due to the size limitation ofthe transmitting window.

Assuming that the receiving side still fails to receive the 23^(rd) and27^(th) PDUs among the transmitted 23^(rd) to 32^(nd) PDUs, and furtherfails to receive the 30^(th) and 31^(st) PDUs. Since the 23^(rd) PDU isnot received, the receiving window, a shown in FIG. 8B, maintains itscurrent range of 23˜33.

Once the status information of the 23^(rd) to 32^(nd) PDUs istransmitted to the transmitting side, the transmitting side deletes thePDUs succeeding in transmission from the buffer. Yet, since the ACK forthe 23^(rd) PDU is not received, updating of the transmitting windowfails to take place like in the receiving side. Hence, the transmittingside, as shown in FIG. 80, re-transmits the 23^(rd), 27^(th), 30^(th),and 31^(st) PDUs while maintaining the transmitting window at a range of23˜33.

If the receiving side keeps failing to receive the 23^(rd) and 27^(th)PDUs, since the 23^(rd) and 27^(th) PDUs remain within the range of thetransmitting window, the transmitting side fails to transmit additionalPDUs, and only re-transmits the 23^(rd) and 27^(th) PDUs. Thereafter,assuming that 23^(rd) and 27^(th) PDUs continue to be re-transmitted,but ultimately fail to be properly transmitted, the transmitting sidethen discards the corresponding SDUs due to the discard timer expirationfor SDU or the maximum (limit) number of re-transmissions has beenreached.

FIG. 9 is a diagram of discontinuously discarding 35^(th), 36^(th),38^(th), and 39^(th) SDUs due to transmission failure of 23^(rd) and27^(th) PDUs. Referring to FIG. 9, in case of discontinuously discardingSDUs, in order to move a receiving window using the MRW procedure, oneof the following two methods is used.

A. Method of Sequentially Executing MRW Procedures as Many Times as theNumber of Sets of Continuously Discarded SDUs

When SDUs are discontinuously discarded, this method regards thecontinuously discarded SDUs as one set, and executes one MRW procedurefor each continuously discarded SDUs set to move a receiving windowsequentially. Namely, referring to FIG. 9, the transmitting side regardsthe 35^(th) and 36^(th) SDUs as one set, and the 38^(th) and 39^(th)SDUs as another set, and then performs the MRW procedure on each of thetwo sets. Since the MRW procedures are performed one-by-one at any onemoment, they cannot be simultaneously executed but is sequentiallyexecuted one after the other. Such a procedure is explained in moredetail by referring to FIG. 10.

First, the transmitting side executes a first MRW procedure while thetransmitting window is between 23˜33. The transmitting side discards allSDUs from the start point of the transmitting window to the 36^(th) SDU,and transmits such information to the receiving side using a MRW command(S1, S2). The receiving side discards all SDUs from the start point ofthe receiving window to the last discarded SDU informed by the receivedMRW command, i.e., the 36^(th) SDU, and then moves the receiving windowto 27˜37 (S3).

Thereafter, the receiving side informs the transmitting side of a movedposition of the receiving window (S4). The transmitting side thenterminates the first MRW procedure and moves the transmitting window to27˜37 in order to correspond with the moved position of the receivingwindow. The transmitting side then executes a second MRW procedure tomove the receiving window after the 39^(th) SDU (S5).

Another MRW command transmitted in the second MRW procedure includes thediscard information of the 39^(th) SDU that is the last discarded SDU ofa second discontinuous discarded SDU set. It should be noted that, sincethe transmitting window is moved to 27˜37 while the second MRW procedureis in progress, the 33^(rd) to 36^(th) PDUs can be transmitted (S6).After discarding all the SDUs from the start point of the receivingwindow to the last discarded SDU informed by the received MRW command,i.e., the 39^(th) SDU, the receiving side moves the start point of thereceiving window to an “appropriate” position between 33˜37 (S7). Inthis case, the 33^(rd) to 36^(th) PDUs can be transmitted while thesecond MRW procedure is performed, whereby the position of the receivingwindow is referred to as being “appropriate” because such positionvaries depending upon whether these PDU are received.

For instance, if there is no additional PDU reception while the secondMRW procedure is in progress, the receiving window is updated to 33˜43.If all of the 33^(rd) to 36^(th) PDUs are received, the receiving windowis updated to 37˜47. Namely, the transmittable PDUs can be transmittedduring the MRW procedure, whereby the reception of such PDUs changes(updates) the position of the receiving window. This is the same as inthe first MRW procedure. Yet, since there are no transmittable PDUsexcept the 23^(rd) and 27^(th) PDUs between the range of 23˜33 of thereceiving window in the example of FIG. 8, the start point of thereceiving window was defined as 27.

After moving the start point of the receiving window to the appropriateposition, the receiving side transmits transmitting window moveinformation to the transmitting side (S8). The transmitting side havingreceived the transmitting window move information terminates the secondMRW procedure and moves the start point of the transmitting window tocorrespond with that of the receiving window (S9). The transmittingwindow is then used to continue transmission from the PDU at the startpoint of the transmitting window (S10).

B. Method of Discarding all PDUs Between Discontinuously Discarded SDUs

FIG. 11 is a flowchart of moving a receiving window using this method(method B) when the discontinuous SDU discard as shown in FIG. 9 takesplace.

In method B, when SDUs are discontinuously discarded, the transmittingside discards all SDUs from one SDU corresponding to the start point ofthe transmitting window up to the last one of the discarded SDUs,regardless of transmission success or failure such that the SDUs fromthe start point of the transmitting window up to last SDU arecontinuously discarded. Namely, if the SDUs are discontinuouslydiscarded as shown in FIG. 9, the transmitting side discards all SDUsfrom the 35^(th) SDU of the start point of the transmitting window up tothe 39^(th) SDU of the last discarded SDU, and sends such information tothe receiving side (S11, S12). In this case, the 37^(th) SDU isdiscarded despite succeeding in transmission. The receiving side havingreceived an MRW command regards all SDUs from the start point of thereceiving window up to the 39^(th) SDU as discarded, so as to discardthe corresponding SDUs, and then moves the receiving window beyond the39^(th) SDU (S13). In this case, the 37^(th) SDU is discarded despitethe transmission success at the transmitting side.

Thereafter, the receiving side informs the transmitting side of themoved position of the receiving window (S14). The transmitting sidehaving received the moved position terminates the MRW procedure andmoves the transmitting window to 33˜44 (S15). The transmitting side thenstarts transmission from the 33^(rd) PDU of the start point of thetransmitting window (S16).

As explained in the above description, when discontinuous SDU discardtakes place, the receiving window is moved by using one of the twomethods, methods A or B in the related art. However, the related artmethods A and B have the following problems or disadvantages.

First, in method A, the MRW procedures are sequentially executed severaltimes to inform the receiving side of the discontinuous SDU discard,whereby considerable time delay takes place in processing subsequentSDUs. Namely, the PDU after the 37^(th) PDU is transmittable after thesecond MRW procedure has been performed in the examples of FIG. 9 andFIG. 10, whereby the SDUs involved in the second MRW procedure should bestored in the RLC buffer for a considerable time. Typically, it takes atleast 150 ms to finish one MRW procedure. If the receiving window ismoved according to method A, the MRW procedure undesirably interruptshigh-speed data communication. When using the SDU discard method basedon the timer scheme, the SDUs fail to be transmitted and continue to bediscarded in the worst-case scenario.

Moreover, in using method B, when the SDUs are discontinuouslydiscarded, the receiving side discards the SDUs that were successfullytransmitted as well, which undesirably reduces transmission efficiency.Namely, in the example of FIG. 9, only the 37^(th) SDU is unnecessarilydiscarded, and thus the transmission efficiency is not greatly reduced.However, in other extreme examples, if the SDUs corresponding to thestart and end points of the transmitting window are discarded, all SDUsin the transmitting window are discarded, which significantly reducestransmission efficiency.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method of moving areceiving window in a wireless mobile communication system thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a method of moving areceiving window in a wireless mobile communication system, whichenables to reduce transmission delay that takes place in case of movingthe receiving window if SDUs are discontinuously discarded.

Another object of the present invention is to provide a method of movinga receiving window in a wireless mobile communication system, whichenables to reduce the degradation of transmission efficiency generatedby moving the receiving window when SDUs are discontinuously discarded.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurposes of the invention, as embodied and broadly described herein, adata communication method according to the present invention includes,receiving a move receiving window (MRW) command; and deliveringsuccessfully received service data units (SDUs) among data units from astart point of a current receiving window to a position indicated by theMRW command to an upper layer.

Preferably, the MRW command is transmitted through a radio environment.

Preferably, the data units are service data units (SDUs) of a data linklayer.

Preferably, the data units are radio link control (RLC) SDUs.

Preferably, the SDUs are identified by a SDU boundary indicator.

Preferably, the SDU boundary indicator is included in a protocol dataunit (PDU) of a data link layer.

Preferably, the SDUs that are not yet successfully received arediscarded.

Preferably, the position that is indicated by the MRW command indicatesan end point of the SDU to be discarded last.

Preferably, the steps are performed in a receive-response mode.

Preferably, the MRW command includes a sequence number of a protocoldata unit (PDU) with an end point of the SDU discarded last; and an endpoint indicator indicating the end point of the SDU in the PDU.

Preferably, the method further comprising moving the receiving window tothe position indicated by the MRW command.

Preferably, the moving of the receiving window is performed in a datalink layer.

In another aspect of the present invention, a method for moving areceiving window in a wireless mobile communication system includesreceiving an information of a last discarded service e data unit (SDU)from a transmitting side; checking whether the SDUs prior to the lastdiscarded service data unit are successfully received; and deliveringthe SDUs that are successfully received to a upper layer and moving areceiving window in accordance with the information.

Preferably, the SDU is a radio link control (RLC) SDU.

Preferably, the information for the last discarded SDU includes asequence number of a protocol data unit (PDU) with an end point of theSDU discarded last; and an end point indicator indicating the end pointof the SDU in the PDU.

Preferably, the moving of the receiving window is performed in a datalink layer.

Preferably, the receiving window moves to the PDU including the endpoint of the last discarded SDU.

Preferably, the SDUs are identified by the end point indicator

Preferably, the checking step comprises identifying data from a portionindicated by one SDU end point indicator to a portion indicated by anadjacent SDU end point indicator as one SDU; and judging thecorresponding SDU as successfully received if all portions of theidentified SDU are received.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a block diagram of an architecture of a radiointerface protocol between a terminal and the UTRAN based on 3GPP radioaccess network standards;

FIG. 2 is a diagram of an example of constructing a PDU from SDU(s);

FIG. 3 is a diagram of explaining the 21^(st) to 23^(rd) AMD PDUs amongthe constructed AMD PDUs in FIG. 2;

FIG. 4 is a diagram showing how the AM RLC constructs an AMD PDU forstoring in transmission and re-transmission buffers;

FIG. 5 is a diagram of an example for transmitting/receiving AMD PDUsand updating transmitting/receiving windows;

FIG. 6 is a diagram of a concept of a construction of a MRW command;

FIG. 7 is a diagram of a MRW command format;

FIGS. 8A to 8C are diagrams of explaining how inconsecutive SDU discardtakes place in normal data transmitting/receiving;

FIG. 9 is a diagram of an example of discarding SDUs discontinuously;

FIG. 10 is a flowchart of a process for moving a receiving window usinga first method according to a related art when discarding SDUsdiscontinuously;

FIG. 11 is a flowchart of a process for moving a receiving window usinga second method according to a related art when discarding SDUsdiscontinuously; and

FIG. 12 is a flowchart of a method for moving a receiving windowaccording to the present invention when discarding SDUs discontinuously.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

The present invention is implemented in a mobile communication systemsuch as a UMTS (universal mobile telecommunications system) developed bythe 3GPP. However, the present invention is further applicable tocommunication systems operating under other standards.

In the present invention, when SDUs are discarded, the AM RLC of thetransmitting side transfers information of the last discarded SDUregardless of the continuity of the discarded SDUs. The AM RLC of thereceiving side then checks whether to receive the SDUs from the startpoint of the receiving window to the last discarded SDU, respectively,and delivers the SDUs that are successfully received to an upper layer,resulting in minimal time delay and minimal reduction of transmissionefficiency even if discontinuous SDU discarding take place.

A detailed embodiment of the present invention is applied to the casewhere SDUs are discarded according to FIG. 9. In this case, it isassumed that the PDU transmitting/receiving process is already inprogress described with respect to FIGS. 8A to 8C.

FIG. 12 is a flow chart of a method for moving a receiving windowaccording to the present invention when discarding SDUs discontinuously.

First, if SDUs are discarded according to FIG. 9, the transmitting sideRLC executes a MRW procedure, and then adds to the MRW command,information of the 39^(th) SDU that is the last one of the discardedSDUs for transmission to the receiving side RLC (S20, S21). In thiscase, the transmitting window lies between the 23^(rd) PDU and the33^(rd) PDU.

If the RLC is set to inform the receiving side of all discarded SDUs,discard information for other SDUs as well as the 39^(th) SDU is carriedon the MRW command. In this case, the 37^(th) SDU is successfullytransmitted and is not discarded. Hence, discard information of the37^(th) SDU is not carried on the MRW command.

Upon receiving the MRW command, the receiving side extracts the discardinformation of the SDU located at a last position in the SDU discardinformation carried on the MRW command. By checking a first PDU SN countfield, the portion of the information of the last discarded SDU can beobtained. In the example of FIG. 9, from the MRW command, the receivingside recognizes the information that the transmitting side discardedSDUs up to a first portion of the 28^(th) PDU.

The receiving side checks all PDUs from the 23^(rd) PDU as the startpoint of the receiving window up to the 28^(th) PDU informed of by theMRW command to determine whether the SDUs are correctly received, andthen selectively discards certain SDUs (S22). The receiving sidedetermines which SDUs have been successfully received by using aboundary indicator, namely, a length indicator (LI) included in a PDUheader.

As the length indicator (LI) indicates the boundary between SDUs, thereceiving side regards a portion between two neighboring LIs to be oneSDU. If there is a portion of a different SDU between two LIs, thereceiving side determines the corresponding SDU as a failure. In oneembodiment of the present invention, as the receiving side receives PDUsin the same manner that shown in FIG. 9, the 23^(rd) and 27^(th) PDUsare not received. Hence, the receiving side determines as follows.

Failing to receive the 23^(rd) PDU, the receiving side considers(recognizes) the latter portion of the 22^(nd) PDU up to a beginningportion of the 25^(th) PDU as one SDU. Since a portion corresponding tothe 23^(rd) PDU of the recognized SDU fails to be received, thereceiving side discards it. The receiving side determines that afollowing portion corresponding to the 37^(th) PDU is successfullyreceived and such is not discarded. Also, the receiving side recognizesthe beginning portion of the 26^(th) PDU up to a beginning portion ofthe 28^(th) PDU as one SDU. The recognized SDU is discarded because aportion corresponding to the 27^(th) PDU has not been properly received.

It is important to note that the receiving side differs from thetransmitting side in calculating the total number of the discarded SDUs,if the MRW command only includes the information of the last discardedSDU. Namely, the transmitting side discards four SDUs in the example ofFIG. 9. Yet, the receiving side regards that only two SDUs arediscarded.

Such a procedure may cause problems in some cases. Thus, if the RLC isset up to deliver the all discarded SDUs information, the transmittingside carries information about each of the discarded SDUs. In this case,the receiving side knows that the end portions of the discarded SDUsexist in the 23^(rd), 25^(th), 27^(th), and 28^(th) PDUs, respectively,whereby it can be seen that four SDUs are discarded in the transmittingside.

The MRW command does not directly deliver the number of the discardedSDUs, but rather, the SN of the PDU having the end portion of thediscarded SDU. This is to inform the receiving side of a position of thediscarded SDU. Namely, in the example of FIG. 9, the receiving sideconsiders that two SDU groups including portions of the 35^(th) and36^(th) SDUs, and the other portions of the 38^(th) and 39^(th) SDUs arediscarded. If the end portions of each of the discarded SDUs in notinformed, but the number of the discarded SDUs is informed, thereceiving side is unable to know how many discarded SDUs exist in thefront and the rear portions. For instance, the receiving side mayconsider that one SDU in the front portion, and three SDUs in the rearportion are discarded or that there are two discarded SDUs in each ofthe front and rear portions. This is related to a sequence of thediscarded SDUs. The discard sequence is significant to some higherlayers. Hence, the MRW command informs the PDU SN indicating where theend portion of each of the discarded SDUs exists.

When the MRW command informs the information of the last discarded SDUor the information of all discarded SDUs, the receiving side discardsportions corresponding to the 35^(th), 36^(th), 38^(th), and 39^(th)SDUs, and delivers the 37^(th) SDU to an upper layer. Also, the RLC ofthe receiving side moves the start point of the receiving window to the33^(rd) PDU to be first received in-sequence.

Thereafter, the receiving side sends information of the start point ofthe moved receiving window to the transmitting side (S23). Thetransmitting side having received such information, determines that theMRW procedure is successfully performed, moves the transmitting windowto the same position as that of the receiving window, and then initiatesa subsequent PDU transmission (S24, S25).

One embodiment of the present invention provides, in a radio accessnetwork, a method of discarding service data units by a sending endemploying a transmission window and a discard trigger. The method cancomprise the steps of, checking all service data units beginning with afirst service data unit located at a lower edge of the transmissionwindow up to a final service data unit that was discarded by the discardtrigger, and discarding those checked service data units that have notbeen positively acknowledged.

Here, the checking step can further comprise a step of positivelyacknowledging any service data units that have been successfully sent toa receiving end.

Also, the above method can further comprise a step of sending, to areceiving end, a command to move a reception window and information ofthe final service data unit.

Another embodiment of the present invention provides, in a radio accessnetwork, a method of discarding service data units by a receiving endemploying a reception window. The method can comprise the steps of,receiving a command to move the reception window, checking all servicedata units beginning with a first service data unit located at a loweredge of the reception window up to a final service data unit indicatedin the command, and discarding those checked service data unit that havenot been successfully received.

Here, this method can further comprise a step of acknowledging, to asending end, any service data units that have been successfullyreceived.

As described above, the receiving side of the present invention checkswhether all SDUs from the start point of the receiving window up to thelast discarded SDU are successfully received, then delivers the SDUsthat are successfully received to an upper layer, and discard only theSDUs that are not successfully received.

A method of moving a receiving window according to the present inventionovercomes the SDU transmission time delay problems created by moving thereceiving window according to the related art, even if the SDUs arediscontinuously discarded.

Moreover, the present invention overcomes the reduction of SDUtransmission efficiency created by the related art method B, therebyenabling improved high-speed data communications, as well as maximizingdata transmission efficiency.

The forgoing embodiments are merely exemplary and are not to beconstrued as limiting the present invention. The present teachings canbe readily applied to other types of apparatuses. The description of thepresent invention is intended to be illustrative, and not to limit thescope of the claims. Many alternatives, modifications, and variationswill be apparent to those skilled in the art.

1. A method for managing a receiving window in a mobile device, the method comprising: for each received data protocol data unit (PDU) having a sequence number which is within a range of the receiving window, which is received from a transmitting side, storing the received data PDU in a buffer, delivering successfully received sequence data units (SDUs) to a higher layer that is stored in the buffer in the order of increasing values of the sequence number and changing the range of the receiving window; and for each control message for shifting a start value of the receiving window, passing at least one successfully received SDU stored in the buffer with a sequence number which is lower than a new start value of the receiving window, as indicated by the control message, up to a higher layer, and setting the new start value of the receiving window to a next value of a sequence number of a last SDU that was passed up to the higher layer.
 2. The method of claim 1, wherein the at least one successfully received SDU is reassembled from the buffered one or more PDUs.
 3. The method of claim 1, for each control message, further comprising setting an end value of the receiving window based on the control message.
 4. The method of claim 1, for each control message, further comprising releasing buffers held by PDUs with sequence numbers that are lower than the new start value.
 5. The method of claim 1, wherein the control message is received if at least one PDU is discarded due to exhausted lifetime of an SDU which is related to at least one PDU at the transmitting side.
 6. The method of claim 1, wherein the data PDUs stored in the buffer are sequentially delivered to the higher layer based on the sequence numbers of the data PDUs.
 7. A mobile communication device for receiving data in a radio communication system, the device comprising: a data receiving unit receiving data protocol data units (PDUs) from a transmitting side, wherein each of the data PDUs has a header including a sequence number; a buffer storing the received data PDUs; a receiving window managing unit setting a receiving window start point based on the sequence number of the received data PDU or a control message for shifting a starting value of a receiving window; and a data processing unit reassembling successfully received service data units (SDUs) from the buffered PDUs for delivery to a higher layer, wherein, for the received control message for shifting a starting value of the receiving window from the transmitting device, the data processing unit checks whether the buffered PDU is a buffered preceding PDU, wherein each of the buffered preceding PDUs has a sequence number that precedes a starting sequence number, and reassembles at least one successfully received SDU from the at least one buffered preceding PDU for delivery to the higher layer, and wherein the receiving window managing unit shifts the starting value of the receiving window to a next value of a sequence number of a last SDU that was reassembled for delivery to the higher layer.
 8. The mobile communication device of claim 7, wherein the receiving window managing unit sets an end value of the receiving window based on the control message.
 9. The mobile communication device of claim 7, wherein for each control message, buffers held by PDUs with sequence numbers that are lower than the new start value are released.
 10. The mobile communication device of claim 7, wherein the control message is received if at least one PDU is discarded due to exhausted lifetime of an SDU which is related to at least one PDU at the transmitting side.
 11. The mobile communication device of claim 7, wherein the data PDUs stored in the buffer are sequentially delivered to the higher layer based on the sequence numbers of the data PDUs. 